Well the force exerted by a spring is simply as follows : Force = Stiffness x Longitudinal displacement from rest position [N] [N/mm] [mm] [lbf] [lbf/inch] [inch] Having the rotation angle of the frame, you could calculate the final frame length where the spring is attached and obtain the displacement. Or you could do the same with the height of the obstacle. The force exerted here however is not constant as it changes in time as the spring compresses and as the velocity of the displacement is damped. What I explained earlier refers to the peak force exerted when the spring is compressed at its maximum. If you would like to study the force cycle, you would have to know the speed of the car, the geometry of the obstacle, the stiffness of the frame assembly and its damping coefficient. You could then plot a second order harmonic equation with the proper parameters.
Thanks for the input, the spring force equasion was something I knew. I think there is a way to simplify what I am trying to envision, I just cant put it to words... -Mark